Spatiotemporal auxin distribution in Arabidopsis tissues is regulated by anabolic and catabolic reactions under long-term ammonium stress

Background The plant hormone auxin is a major coordinator of plant growth and development in response to diverse environmental signals, including nutritional conditions. Sole ammonium (NH 4 + ) nutrition is one of the unique growth-suppressing conditions for plants. Therefore, the quest to understand NH 4 + -mediated developmental defects led us to analyze auxin metabolism. Results Indole-3-acetic acid (IAA), the most predominant natural auxin, accumulates in the leaves and roots of mature Arabidopsis thaliana plants grown on NH 4 + , but not in the root tips. We found changes at the expressional level in reactions leading to IAA biosynthesis and deactivation in different tissues. Finally, NH 4 + nutrition would facilitate the formation of inactive oxidized IAA as the final product. Conclusions NH 4 + -mediated accelerated auxin turnover rates implicate transient and local IAA peaks. A noticeable auxin pattern in tissues correlates with the developmental adaptations of the short and highly branched root system of NH 4 + -grown plants. Therefore, the spatiotemporal distribution of auxin might be a root-shaping signal specific to adjust to NH 4 + -stress conditions.